1. Technical Field
The invention relates generally to semiconductor devices and more specifically to a semiconductor gate structure for a silicon-on-insulator (SOI) semiconductor device.
2. Related Art
To form a four-terminal (source, drain, gate, body) semiconductor device in bulk technology, electrical connection is typically made via the substrate to the body region. The body bias is relatively fixed for all bias conditions. Comparatively, the body region of a conventional SOI semiconductor device is isolated from the substrate by the underlying insulator. Thus, conventional SOI semiconductor devices typically have three terminals (source, drain, gate) with the body region of the SOI semiconductor devices either being coupled to the source/drain terminals, coupled to the backgate of the body region, or not coupled at all (electrically floating). In the aforementioned cases, the body bias is generally not fixed for all bias conditions. That is, if the body region electrically floats, the body bias of the body region is normally dependent on the terminal biases. The coupling of the body region to any other region also results in a modified device behavior when compared to the expected behavior of a fixed body bias.
Contact to the body region of an SOI semiconductor device is needed to form a four-terminal SOI semiconductor device. Such four-terminal semiconductor devices provide a fixed body bias and are analogous to a bulk semiconductor device, except that bulk semiconductor devices generally have very low series resistance between the body contact and the actual body region of the device. In four-terminal SOI semiconductor devices heretofore known, control of the body region voltage is accomplished through either contacting the body region at the edge of the semiconductor device, or providing a semiconductor contact region at the surface of the semiconductor device that may be used to contact and control the voltage of the body region. One example of the latter case is an H-gate semiconductor device. Contacting the body region through a semiconductor device such as an H-gate semiconductor device provides accurate control voltage only at the points proximate the contact. The resistance to any point of the body region increases with distance away from the contact. Therefore, any current provided through the contact will cause a corresponding increase in series resistance across the body region at distances away from the contact. As a result, a single contact does not provide a low series resistance and consequently, does not provide a uniform voltage across the entire body region for either testing or operation of the four-terminal semiconductor device. Accordingly, a need has developed in the art for a structure and method that will provide a substantially uniform voltage across the body region in a four-terminal SOI semiconductor device.